A turbofan of an aircraft comprises, in a known manner, a primary gas flow path and a secondary gas flow path which are separated by an inter-flow path compartment of a casing known as an “inter-turbine casing”. In the primary flow path are arranged, from upstream to downstream in the gas flow direction, a low-pressure compressor and a high-pressure compressor. The air thus compressed is brought to a combustion chamber in which it is mixed with pressurized fuel which is burned so that, downstream of the combustion chamber, energy is supplied to a high-pressure turbine which drives the high-pressure compressor, and to a low-pressure turbine which drives the fan and the low-pressure compressor. The gases leaving the turbines provide a residual thrust which combines with the thrust generated by the gases circulating in the secondary flow path to propel the aircraft.
FIG. 1 schematically illustrates a known architecture for the turbines of a turbofan. The low-pressure turbine 10 comprises stator blades 12 and rotor blades 14. The rotor blades 14 drive a shaft 16 rotating in a bearing 18 which, at the downstream end of said low-pressure turbine 10, is supported by an exhaust casing 20 extending radially to the outer casing 22. The high-pressure turbine 24 comprises stator blades 26 and rotor blades 28. The rotor blades 28 drive a shaft 30 rotating in a bearing 32 which, at the upstream end of the low-pressure turbine 10, is supported by an inter-turbine casing 40 extending radially to the outer casing 22, in the inter-turbine space 34. Such a turbine architecture, in which the high-pressure turbine is held on the stator of the low-pressure turbine, has the known advantage of allowing improved control of the relative movements of the two turbines, thereby reducing the operational clearances in relation to other turbine architectures.
The inter-turbine casing 40 is a structural component which comprises, in a known manner, an outer ring forming part of the outer casing and an inner ring forming part of the inner casing or hub on which the high-pressure turbine shaft bearing support is fastened. The inter-turbine casing also comprises a certain number of radial arms, which are structural components connecting the outer ring and the inner ring. It also comprises fairings 42 having a profiled shape which are arranged in the aerodynamic air duct so as to distribute the air stream coming from the high-pressure turbine before it reaches the first stage of the low-pressure turbine. The radial arms are preferably arranged inside some of these fairings, or in all of these fairings.
The thermally stressed components such as the turbine rotors, the fairings and the radial arms need to be cooled. For this purpose, it is known practice for cooling air bled from a cooler part of the turbofan to be fed through the outer ring, the fairings and the inner rings. However, on account of the expansions to which the components are subjected during operation, the fairings are divided into sectors, thus allowing an operating clearance between the various sectors. These operating clearances are, however, also sources of unwanted leaks through which some of the cooling air escapes. Such leaks cause a shortfall in the cooling circuit performance, since the quantity of cooling air is not optimized. There results a reduction in the life of the cooled components or the need to increase the flow rate of the cooling air.